Multiple gear change gear unit, especially those having wide gear spacing, make possible in motor vehicles having internal combustion engines, on the one hand, favorable life and on the other an economic consumption of fuel, since for each operating state it is possible to select a favorable working range of the internal combustion engine. In passenger cars unitary transmissions with four to five gears while in commercial vehicles there are used multiple gear units providing up to eighteen gears.
A transmission of planetary design having a multiple gear main gear unit and a two-gear secondary gear unit designed as splitter gear which in the course of a gear change sequence is shifted once, has been disclosed in EP B1 214 989. With said gear unit five forward gears can be shifted, the gear shift of the gear unit being comparatively easy, since shifting components only have to be actuated either in the main gear unit or in the group gear unit.
From the applicant's DE 42 34 572 has become known a change gear unit of group design in which the ratio steps between the lower gears are larger than between the upper gears and which works in combination with the lower and upper gears as a splitter group gear unit while in combination with the middle gears works as range group gear unit. Here is required in the middle gear range a group gearshift which coincides with a gearshift in the main gear unit so that a special electronic start up is required. According to a special embodiment the gear unit has a planetary design with wheel sets for a six-gear to eight-gear unit.
The applicant's DE 31 33 067 describes a gear shiftable change gear unit which consists of one multiple gear main unit and fitted downstream thereof a splitter group with two input gears of which one is connectable with the input shaft of the gear unit and the other is optionally connectable also with a main shaft of the gear unit. The splitter group forms here a firm component part of the main gear unit and it can be bridged so that the gears of the main unit can be shifted directly to the main shaft by the input shaft by alternate introduction of a double clutch and other separating clutches.
A gear change gear unit which has a main unit situated on the input side, a range group gear unit and a reverse gear unit situated on the output side and is shiftable with the twelve forward gears has been disclosed in the applicant's DE 36 19 329. This change gear unit is adequate for commercial vehicles, for example, agricultural tractors, since it is possible when under load to shift from gear to gear so that even during a change of gear power is uninterruptedly transmitted from the input shaft to the output shaft. This change gear unit is especially well suited to agricultural tractors which, in their main drive speed range (medium drive speeds), are to have a high degree of power utilization (defined as the ratio of the actual power to the highest power) and/or a high working efficiency (defined as the ratio of useful work to fuel consumption) while the degree of usefulness and the degree of efficiency in low and high drive speeds are of less importance.
In such known gear change units, there are situated in a main axle an input shaft, a double clutch, a first intermediate shaft of a first part of a main gear unit, a second intermediate shaft of a second part of the main gear unit and a third intermediate shaft which belongs both to a range group gear unit and to a reverse gear unit. Further provided are two parallel shafts which support a plurality of gears.
In the applicant's DE 40 20 558 is described a multiple gear change gear unit in which between the input group and a main group is situated an intermediate gear unit; this change gear unit, is especially suited to tractors and certain construction vehicles, has a wide range of ratios with many ratio steps which make possible an optimal utilization of the innate engine traction at all drive speeds. In a special development of the intermediate gear unit, it serves as overdrive, having a certain reduction ratio so that high speeds can be achieved without having to give up low speeds for working purposes.
The importance of operating comfort which is function of the shifting force and thus of the shifting stroke to be applied, and noise developed due, for example, to so-called idle speed rattle associated with manually shiftable multiple gear units for trucks, has increased in the last few years and has become increasingly decisive in buyers, purchasers. The quality of a gear change unit, in view of this criteria, has become important in the design of gear units, that is, in the arrangement of the wheels, shafts and shifting components.
A reduction of shifting force and shifting stroke can be achieved by the rotary masses which have to be synchronized during a gearshift operations being as small as possible. The lowest possible noise level at idle speed (slight idle speed rattle) can be obtained by ensuring that rotation irregularities are not introduced in the gear unit.